(CNN) --Building on his momentum, Sen. John Kerry picked up five of the seven states holding contests for the Democratic presidential nomination Tuesday. Sen. John Edwards kept his White House dream alive with a win in South Carolina and a surprisingly strong showing in Oklahoma.

"We will take nothing for granted. We will compete everywhere. And in November, we will beat George W. Bush," Kerry told supporters gathered in Seattle, Washington, where caucuses are scheduled Saturday.

The verdict was bitter for Sen. Joe Lieberman of Connecticut. The 2000 vice presidential nominee withdrew from the race after failing to win any state, even Delaware, where he had concentrated his campaign recently.

"I have decided tonight to end my quest for the presidency," a gracious Lieberman told supporters at a meeting in Arlington, Virginia, calling it a "difficult, but realistic decision."

The results provided little encouragement to former Vermont Gov. Howard Dean, once viewed as the man to beat for the Democratic nomination. He failed to pick up a single first-place finish, and he has yet to win a single primary or caucus.

The victories for Kerry -- a 19-year veteran of the Senate from Massachusetts -- in Arizona, Delaware, Missouri, North Dakota and New Mexico strengthened his status as the front-runner. (CNN.com's interactive Election Calendar)

The margins of victory were wide for Kerry in Arizona, Delaware, New Mexico and Missouri -- the night's biggest prize with 74 delegates.

Clark leads in Oklahoma

In Oklahoma, retired Army Gen. Wesley Clark held a slight lead over Edwards with all precincts reporting. But the race was so close that no winner could be declared until the vote is certified by state elections board next week. Kerry was third.

Nevertheless, Clark claimed victory in Oklahoma, telling supporters he "couldn't be prouder" of winning his first election.

Edwards, a first-term senator from North Carolina, said his South Carolina victory and strong showing in Oklahoma showed he had broad appeal.

"I think South Carolina is a great test for winning in the South, winning among rural voters and winning among the African-American voters," an ebullient Edwards told CNN after addressing supporters in Columbia, South Carolina.

Edwards had campaigned heavily in South Carolina, whose primary is known as the gateway to the South. A native of that state, Edwards stressed his Southern roots and said the South is critical for Democrats if they are serious about defeating President Bush in November.

"We're second in Missouri, and in a hot contest for first in Oklahoma," Edwards said. "So this is a huge night for us."

Exit polls indicated the economy was a key issue for voters in the primary states, suggesting Democrats will continue to hit Bush on his stewardship of the nation's fiscal house.

Tuesday's contests extended west and south and involved far more minorities than in the earlier contests in Iowa and New Hampshire. African-American voters, for example, were a significant voting bloc in South Carolina, and Hispanic voters were a factor in Arizona and New Mexico.

The Rev. Al Sharpton, the lone black candidate in the Democratic field, did not claim either first or second in South Carolina, despite spending a great deal of time in the state.

Still, Sharpton was upbeat about the night's results, proclaiming he had exceeded expectations. "I'm very satisfied," Sharpton said.

Dean's challenge

Dean scaled back his efforts in South Carolina and other February 3 contests after disappointing defeats in Iowa and New Hampshire. Addressing supporters in Washington state Tuesday night, Dean vowed to stay in the race.

"This is all about who gets the most delegates in Boston in July, and it's going to be us," Dean told supporters, referring to the city where Democrats will gather for the nominating convention.

CNN estimates that Kerry will end up with about half of the 269 delegates at stake Tuesday, and Edwards is likely to get about a quarter. A total of 2,161 delegates are needed to win the nomination at the Democratic National Convention in July. (Where things stand: A delegate scorecard)

The sixth Democrat remaining in the race, Rep. Dennis Kucinich of Ohio, trailed badly in all seven states on Tuesday.

Lieberman's decision to drop out of the race follows similar moves by Rep. Dick Gephardt and former Sen. Carol Moseley Braun as the primary season heated up.